Within the electrophysiology art, it is well known to provide an expandable "basket assembly" carrying multiple electrodes on the distal end of a catheter for use in a variety of diagnostic and other procedures within the heart. For example, the Constellation.TM. catheter manufactured by the assignee of the present application includes a distally mounted basket assembly formed by a plurality of circular spline elements attached at both ends to a catheter, i.e., such that each spline element forms a loop at the catheter end. The spline elements are generally rectangular and are made of a highly flexible metal alloy, e.g. Nitinol, which has well known shape memory properties. In particular, the spline elements are attached to the catheter end in an evenly spaced relationship, aligned like the lines of longitude on a globe.
The spline elements are joined distally, i.e., at their midpoints, by a cylindrical metal tip member. The distal tip member has a plurality of passages extending through the cylindrical body perpendicular to its longitudinal axis and spaced apart from one another. The passages intersect the longitudinal axis such that the passages are circumferentially spaced evenly about the longitudinal axis, i.e. to define evenly distributed lines of longitude on the globe.
During assembly, the spline elements are individually directed through respective passages in the tip member until their midpoints intersect the longitudinal axis, i.e., prior to being attached to the end of the catheter. Each passage includes a recess for securing a notch formed at the midpoint of the respective spline element. Thus, the cooperating notches and recesses hold the spline elements and keep them from sliding out of the passages and becoming misaligned, while still allowing for bending.
During use, the basket assembly is directed between contracted and expanded conditions. In particular, the spline elements are compressed into a contracted condition as the assembly is moved through a guide sheath for introduction into a patient's body, e.g. through the cardiovascular system. The basket assembly is deployed at a target site within the body, e.g. within a heart chamber, wherein the guide sheath is pulled back, allowing the spline elements to return to their expanded condition for use, for example, during a diagnostic procedure. During the procedure, the basket assembly may also be at least partially contracted and expanded repeatedly, for example, as a result of the beating of the heart.
To minimize the stress experienced by the spline elements during expansion and contraction, each spline element preferably defines an individual "bridge," i.e., each spline element is independently supported between the catheter body and the distal tip member, isolated from one another. For this reason, each passage through the tip member includes elongate entry slots extending parallel to the longitudinal axis of the distal tip to allow for some radial movement of the spline elements during expansion and contraction, but still restrain their movement circumferentially about the longitudinal axis.
Because of the relatively small sizes and tight tolerances required, the distal tip members are constructed using high precision computer-controlled tools. Cylindrical blanks are first machined, and then the individual passages are machined through the blanks to produce the finished desired tips. This manufacturing process requires machining the first passage, including the required recess and/or elongate slots, indexing the cylindrical body both radially and axially, and then repeating the process sequentially for each additional passage. Thus, the Constellation.TM. distal tips are highly specialized and relatively expensive components to manufacture.
Accordingly, it would be desirable to provide a distal tip for basket assemblies that may be less expensive and/or easier to make.